The present invention relates to a vehicle wheel that is provided with a pneumatic tire and that has means for providing information. Furthermore, the present invention relates to a method and apparatus for producing a tire for such a vehicle wheel.
The patents DE-195 03 468 and -9 disclose wheel bearing seal arrangements that have magnetizable elastomeric material and, to detect the rotation, are provided with a multi-pole ring that is disposed across from a sensor secured to the chassis.
EP 0 378 939 similarly describes a rotating seal having a magnetic coding as an indicator.
Aside from general shortcomings, such means for indicating the number of turns have the general drawback that they are not suitable for determining the information that is of interest for regulating slipping or sliding using the longitudinal forces that act upon the vehicle wheel.
In addition, the subject matter of the aforementioned documents are in principle not suitable for contributing any suggestion to the present invention.
The application PCT/EP95/03864 discloses a measuring system for detecting the longitudinal force of the tire and/or the tire deformation that is caused by the wheel load. The present invention is intended to serve in particular for the further development of this promising system.
It is an object of the present invention to provide a vehicle wheel that is provided with a pneumatic (rubber) tire, with the aid of which the information required for operating a modern vehicle, e.g. wheel rotational speed for ABS (anti-lock brake system) and/or longitudinal forces (torsional forces) that act upon the tire for regulating slipping, can be made available. In particular, a high level of security against vandalism and sabotage is to be achieved.
This object is realized in that the tire of the vehicle wheel, at least at one predetermined location, contains a rubber mixture that is permeated with magnetizable particles. These magnetizable locations, e.g. an annular band in the sidewall of the tire, should in the longitudinal or peripheral direction have successive zones of different, which includes zero, magnetization (e.g. bar codes) in one or more rows, wherein if two or more rows are provided, the rows are disposed at different radii along the peripheral direction of the tire. Thus with the aid of a sensor that is secured to the chassis, not only can the rotational speed and direction of rotation of the respective wheel be provided, but rather while additionally avoiding a reading row of the bar code that is disposed further radially inwardly, in place thereof or in addition thereto time intervals between the passive outer and inner marks can be measured, the lengths of which correlate with the desired information for longitudinal force andlor tire deflection.
In the magnetized zones, the magnetic lines of flux preferably extend in the peripheral direction. In this connection, a signal spacing is achieved by different orientation or alignment of the lines of flux (polarity).
A further object of the present invention is to provide a method and a related apparatus for producing an inventive tire.
The method essentially comprises introducing ferromagnetic particles into the rubber mixture, preferably in the vicinity of the sidewall of the tire, and magnetizing zones of such ferromagnetic particles in the peripheral direction of the tire with alternating polarity, or magnetizing some particle zones and not others. In either case, distinct differences will exist from zone to zone. The magnetization is preferably achieved by means of magnetic lines of flux that extend in the peripheral direction. The rubber mixture is, for example, in the form of an annular band obtained by either a straight extrusion or a straight calenderation aligning the magnetizable particles in the direction of extrusion or calenderation and by forming the straight band into the annular band.
The polarization, which varies over the periphery, preferably alternating, is preferably effected after installation of the band that contains the magnetizable particles into the green tire, and in addition preferably after vulcanization thereof. More preferably, the polarization is effected after the tire is delivered to a customer, and most preferably only shortly prior to mounting of the tire on a wheel, so that the signal sequence stored in the tire in at least one row on at least one sidewall of the tire can be set precisely to the requirements of a vehicle that is to be equipped with the tire.
The inventive method can be carried out with an apparatus that comprises field coils that are disposed in the peripheral direction of the tire and are embodied in the form of two half coils; the field or magnetizing coils can be disposed in the inner and outer sides of the tire at the location of the magnetizable regions, and can have supplied thereto electrical current. For this purpose, the two half coils are movably interconnected by electrical lines. So that a closed circuit is formed, an electrical connection exists between in each case two coils in which oppositely connected magnetic fields are built up, while axially extending magnetic lines of flux can be simply generated by conventional magnets, allowing the aforementioned apparatus to generate lines of flux that extend in the peripheral direction of the tire. The polarized zones produced in the tire then similarly have lines of flux that extend in the peripheral direction, as a result of which the signals can be detected particularly reliably and easily by sensors that are preferably arranged in such a way that they follow the spring movements of the wheel suspension and pivoting movements due steering.
If the physical arrangement is such that the lines that run back and forth between the two coils are physically closely adjacent between the two coils, especially preferably snaked together, the magnetic fields that are generated by the current in these connecting lines are nearly eliminated.
The apparatus can comprise a plurality of coil pairs. Complicated wiring between the coils is then also possible, but always reverts to the same principle.
Any sequence of differing magnetization may include some distance or space between consecutive zones of differing magnetization resulting in intermediate zones of zero magnetization. Thus, the wording xe2x80x9ctwo zones are differently magnetizedxe2x80x9d includes the case where one of these zones is magnetized and the other is not magnetized.
To additionally recognize the direction of rotation of a tire, it is necessary to provide a pattern or sequence of differing magnetization which is asymmetrical along the peripheral direction. The object of such an asymmetry is that a different sequence is provided depending upon whether the zones of differing magnetization are read forward or backward. To accomplish this, it is necessary to provide three successive zones that are all different from one another.
For attaining a strong and cost-efficient magnetization, it is preferred to use anywhere only such pairs of coils explained before. Any pair of coils results in a part-sequence of polarization as NSSN or SNNS, wherein xe2x80x9cSxe2x80x9d is used for a south-pole and xe2x80x9cNxe2x80x9d for a northpole. For receivingxe2x80x94using such pairs of coilsxe2x80x94not only two but three different zones of magnetization, there should be inserted anywhere between different coils orxe2x80x94preferrablyxe2x80x94between different pairs of coils a space of zero magnetization, addressed in the following by the symbol xe2x80x9c0xe2x80x9d. Thus, such a direction-determining part of a sequence of polarization may be NOS or vice versa. The important thing is that the entire sequence must on the whole be asymmetrical so that it reads differently forward than backward.
Such a sequence may be: NSSN0SNNSSNNS,NSSN0SNNSSNNS,NSSN0SNNSSNNS, . . . In this example the direction-determining parts of the sequence are underligned. The inserted commas should only help to recognize the repeating periods; they do not represent a space of zero magnetization.
The shape of the coils can be adapted to the tire contour. One of the coil halves can be rigidly mounted.
Preferably after the vulcanization of the tire, the proposed apparatus serves for the inhomogeneous, in the peripheral direction of the tire, magnetization of hard magnetic particles that are previously introduced into a region of the tire sidewall. Hard magnetic particles are preferred over soft magnetic particles because the polarity thereof can be changed only with difficulty and therefore makes vandalism and sabotage more difficult. This involves the problem that in order to receive the desired magnetization, very strong magnetic fields are required; even these strong fields are made available by the aforementioned apparatus.
Such an alignment of the magnetization in the peripheral direction minimizes the diminishing of the magnetic polarization in the particles due to the field of the adjacent particles. A demagnetization would be particularly great for laminar magnets that are magnetized perpendicular to the surface, in other words with axial lines of flux.
If the connecting line between the coil pairs is flexible, the distance or spacing between the coils can be varied. This is of particular interest for the establishment of a bar code, and permits the formation of additional zones.
The apparatus is preferably embodied in such a way that it is possible to produce therewith a magnetic field that periodically varies in the peripheral direction so that regions with oppositely directed magnetization alternate with one another, or regions or zones of magnetization alternate or are separated from one another by zones or spaces of zero magnetization. The thus generated magnetization and the spatial magnetization differences can be detected with magnetic field sensors and can serve as input signals for slip regulating systems, especially also for SWT systems (sidewall torsion measuring systems).
The hard magnetic particles that are to be introduced into the tire preferably comprised hard ferrites and neodymium iron borides. In the magnetized state they have a maximum coercive field strength of about 10,000 A/cm. Such particles are preferably homogeneously distributed in the peripheral direction. In order to align the magnetic moments in these materials, magnetic fields of the order of magnitude of several Teslas are required. For this purpose, a winding turn density of 100/cm is required for a coil at, for example, a current intensity of 100 A. To achieve as great a field strength as possible in the outer space it is additionally necessary that the moments be aligned in the peripheral direction. In this case after all demagnetization effects (xe2x80x9cmagnetic short circuitsxe2x80x9d) are particularly small. Demagnetization here means the self attenuation of a magnet due to its own magnetic field, which is particularly directed opposite to the xe2x80x9cmomentsxe2x80x9d. The effect is a function of geometry and, for example for plates where the magnetization is perpendicular to the plane, is particularly great The term hard ferrites is used in this application to mean a hard ferromagnetic ferrite, and in particular an oxide ceramic material of the general formula Me11O.Fe2O3, where Me11 is a bivalent metal, such as barium, strontium, and iron, by way of example.
Soft magnetic materials, which in principle can have similar magnitude residual fields as do hard magnetic materials but have considerably smaller coercive field strengths, are less suitable for a tire that is to be used pursuant to the present invention. Although soft magnetic materials are easier to magnetize, they also lose their magnetization easier, for example in external magnetic fields or due to impacts. In addition, already with slight criminal energy they enable the manipulation of the magnetic code.
In order to be able to detect a change of the time span between the passes of the two marks (in one row for ABS or in two rows for SWT) as precisely as possible, it is desired that the magnetization in the peripheral direction be effected as quadrilaterally as possible, i.e. that the magnetization should be substantially homogeneous within a cohesive region (code bars), and above all at the boundaries of this region should change with as great a gradient as possible. For the conventional ABS systems that detect the wheel rotations it is, in contrast, sufficient if the magnetization in the peripheral direction of the tire be effected in a sinusoidal manner.
In principle, it would be simpler to magnetize the semifinished product that is installed in the tire sidewall prior to build-up of the tire, and to install such magnetized pieces. With this method, there resulted at the respective abutment or contact areas irregularities in the magnetization and air pockets in the green tire. In addition, problems resulted due to the bulging process of the tire. At least one class of compounds having very high residual magnetism (neodymium iron borides) degrades starting at temperatures greater than about 120xc2x0 C., i.e. the magnetization of particles of this material decreases irreversibly so that the tire vulcanization, which is frequently carried out at temperatures of between 160xc2x0 C. to 200xc2x0 C., stands in the way of the use of these materials.
For this reason, in the event that neodymium iron borides are to be used, the magnetization of the tire sidewall must be effected after the vulcanization.
Although other hard ferrites can be exposed to this temperature without degradation of the magnetic properties, a disorientation or disalignment of the particles in the rubber mixture can occur due to the flow processes, so that the macroscopic magnetization of a zone(region) decreases, although the magnetization of the particles is not affected. For this reason, even when using these other hard ferrites that are known to the expert the magnetization is preferably carried out after the vulcanization.
In contrast to the wheel bearing seals, pursuant to the present invention the magnetizable regions are disposed in the interior of the tire rubber, so that the minimum distance between the coil wires and the region that is to be magnetized is considerably greater. The field intensity generated by a coil is inversely proportional to the distance from the wire and is therefore reduced in the same proportion as the increase in the distance. The preferred length in the peripheral direction of a homogeneously magnetized region(pole) on the inventive tire is approximately as great as with the known wheel bearing seals and therefore, when the magnetization is effected at the end of the tire production process, produces a satisfactorily strong signal when it passes a sensor in relationship to the expended current intensity. In contrast thereto, merely multiplying the number of wires would lead to an extremely high consumption of energy accompanied by not having an optimum homogeneity of the magnetization within a pole.
Due to the high field intensity required for the magnetization, a correspondingly high number of ampere turns is required. For this reason, a coil-type arrangement is selected.
With the simplest approach of disposing two field or magnetizing coils on both sides of the tire sidewall, with the axes of the coils parallel to the peripheral direction, there is achieved in the region that is to be magnetized only a weak magnetic field in relation to the field intensity in the coils. To increase the strength it is therefore necessary to not return the current at a distance from the tire, but rather to dispose the wires in the vicinity of the tire so that the field becomes maximum in the tire sidewall.
An alternative approach for achieving as homogeneous a field in the peripheral direction as possible in the regions(poles) that are to be magnetized while at the same time not having to take into account great losses during the magnetization, is provided with an arrangement where the field that is generated by the connecting wires between the coils is compensated by an equal magnitude current that however flows in the opposite direction. This arrangement can also be combined with the aforementioned arrangement, e.g. only for the inner connecting wires.